1. Field of the Invention
The present invention relates to a microwave heating device with high heating efficiency. The present invention also relates to an image fixing apparatus which uses such microwave heating device with high heating efficiency for fusing developing particles (toner).
2. Description of the Related Art
An image fixing apparatus fuses a toner material onto a sheet (object to be printed) to fix an image onto a sheet. A conventional image fixing apparatus applies heat or pressure onto the sheet by means of a fusing roller to fuse toner onto the sheet.
However, in the conventional configuration, the fusing roller wears with time. As a method for solving such a problem, a non-contact type method for fusing toner with a microwave has been developed in recent years (for example, see JP-A-2003-295692).
FIGS. 23A and 23B are conceptual diagrams showing a configuration of a microwave device disclosed in JP-A-2003-295692.
As shown in FIG. 23A, a microwave device 100 includes a magnetron 110 generating a microwave, an input coupling converter 113 which input couples the microwave generated from the magnetron 110 to a resonator chamber 103, a water reservoir 111, and a circulator 112. Between the input coupling converter 113 and the resonator chamber 103, a coupling aperture 114 with a diaphragm is provided. The resonator chamber 103 has a side surface 109 provided with a passing portion 107 for passing and guiding a sheet 101 therethrough. The resonator chamber 103 has on the downstream side a terminal end slider 115 made of metal. The terminal end, slider 115 is horizontally movable relative to the resonator chamber 103, and extends into the resonator chamber 103.
FIG. 23B is a schematic perspective view of the resonator chamber 103 portion. A microwave generated from the magnetron 110 is led into the resonator chamber 103. For understanding, FIG. 23B shows the microwave in a substantially sine wave form.
The resonator chamber 103 has the side surface 109 and a side surface 109′ which are opposite to each other and are provided with the passing portion 107 and a passing portion 107′, respectively. The sheet 101 passes through the passing portion 107′, and is led into the resonator chamber 103. Then, the sheet 101 passes through the passing portion 107 opposite to the passing portion 107′, and is ejected therefrom. The moving direction of the sheet 101 is indicated by an arrow.
The passing portions 107 and 107′ include therein a movable element 104. The element 104 is a bar made of polytetrafluoroethylene (PTFE), and extends into the resonator chamber 103.
In JP-A-2003-295692, the position of the element 104 can be longitudinally moved in the resonator chamber 103. The position of the element 104 is moved to regulate the resonance conditions in the resonator chamber 103. Therefore, the microwave absorption onto the sheet 101 can be enhanced.
In the technique of JP-A-2003-295692, the coupling aperture 114 with a diaphragm is provided between the input coupling converter 113 and the resonator chamber 103. Thereby, a standing wave is formed in the resonator chamber 103. However, the diaphragm portion has an inclined side surface which causes microwave reflection, thereby lowering transmission efficiency. That is, to lead a high-energy microwave into the chamber, it is necessary to generate higher microwave energy from the magnetron. As a result, the energy consumption is increased.
In the microwave field, it has been known that the temperature of a microwave-exposed sheet is increased. However, in an application in which it is necessary to fuse toner onto a sheet in a very short time in, e.g., a printer and a copier, a method which enables temperature increase only for fusing toner in such a short time cannot be established at present. As a typical example of electronic equipment which performs heating with a microwave, e.g., a microwave oven has been known. However, even when a sheet put into an electronic oven is applied with a microwave for one to about several seconds, the temperature of the sheet cannot be increased by 100° C. or more.
In the technique of JP-A-2003-295692, it is difficult to fuse toner in a very short time. In addition, to shorten the fusing time by using the technique, it is necessary to generate very high microwave energy from the magnetron.